I guess I have 3 things. Google Dado blade in EU, especially do a You Tube type search, and you will find many videos from guys over there scoffing at the "illegality" of using a Dado stack over there, and showing what they do. You might get some ideas.
Well 4 things. Looking at the videos I would guess you are seeing 5/8" arbor holes. You might go to Mike, or Jonathans sites and see if they spec one with a bigger hole. I know from experience that the quickest way to get a really wonky sawblade is to try to drill out the arbor hole of an existing blade. Friend who owns a specialty tool shop here, all of the requisite equipment, and they were fractionally off. It was a case of you could see the movement, and it wasn't of the confidence giving type. Runout is just a word, till you really see it in action.. :-O